Debris litters fields around a fertilizer plant in West, Texas, on Thursday, April 18, 2013. Much of the small town suffered damage when the plant caught fire causing a massive explosion Wednesday night. Authorities are still trying to determine the death and injury toll.

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(CNN) – Welcome to CNN Radio News Day.

Search and rescue efforts continue today in West, Texas. Much of the small town was flattened last night by a huge explosion at a fertilizer plant. It was a blast so strong it registered as a magnitude 2.1 earthquake. A number of first responders, including firefighters, were already at the plant, battling a fire that broke-out hours earlier. As many as 15 people are estimated dead, with more than 160 hurt. A dangerous component of fertilizer production is commercial nitrogen. Emory University chemistry professor Doug Mulford says it's the process to isolate usable nitrogen that's tricky, even though it's all around us:

"We have to get it in a form that usable, and that's what they were doing at the West, Texas plant and other chemical fertilizer plants."

The most watched debate of the year – over gun legislation – has now ground to a halt. It's at a standstill, at least for now, after a series of votes in the past day. None of the major plans, including an idea to expand background checks, could get the 60 votes needed to move ahead Wednesday. So is the gun debate actually over? Not according to Dudley Brown, who's the executive director of the National Association for Gun Rights:

"We don't think this has stopped and we're not about ready to walk away from the fight. We don't think we've won. We need some vigilant action."

President Obama was in Boston today to honor the victims of the marathon bombings. He spoke at an interfaith service encouraging those in attendance to carry on in the face of fear. As the people of Boston paused today, to mourn, and heal – behind the scenes the search for the person, or people, responsible for the deadly terror attack continues. CNN's Debroah Feyerick says investigators continue to pour through surveillance video and pictures taken that day:

“There are a number of images of people who they're very interested in talking to – who investigators are very interested in speaking with. What they're trying to do is... rule people out. It's just a question of looking at images, seeing what behaviors seem normal and what behaviors seem abnormal.”